Cast Shard of the Nightbringer by paying ({5} magic symbol) ({B} magic symbol) ({B} magic symbol) ({B} magic symbol) .
Shard of the Nightbringer triggers, causing an opponent to lose half their life total, rounded up, and you to gain life equal to the life lost this way.
At the beginning of your end step, Warlock Class triggers, causing each opponent to lose life equal to the life they lost this turn.
The opponent targeted in step 2 loses the game due to having zero or less life.